17/08/2012

Update on myDAQ accoustics - myBAT

This week we started on Subsonic signals, we have a simple labVIEW program but we still need to find a efficient way of analyzing subsonic signals. 










In this part of the project we are using the speaker as a microphone.  As you can see, the picture above shows the sub woofer with a mass in the centre, this is to improve its low frequency operation and also the heavier the mass the lower resonant frequency is.  The second picture shows the speaker bolted to 4 columns which are fixed to a square piece of wood, this is so there is a better connection on capturing infrasonic vibrations as there is a larger surface area. 

We have attempted various experiments and using the lift in the Sackville Street building we got a constant frequency of 9.94 Hz.  The other experiments had large variations in the captured frequency and showed no reliable results thus pushing us further to improve the labVIEW program.

10/08/2012

Video of Batector in action


Rail gun

So today we were in a Friday evening mood and decided to try to attempt building a rail gun with Abhi's coils and several power sources. This is picture of our set up:



We had 4 power sources and used only one or two coils instead of three. This was the result of the experiment:




09/08/2012

Update on myDAQ accoustics - myBAT


This week we started testing our PCB’s.  However we came across many problems.  The first being that there were some occurrences where the manufacturing process had not connected the wires in the right places.  As you can see below we had to add wires in ourselves to connect some of the components correctly.


1.      This wire connects the power terminal to the VCO 
2.      Pin 11 on the VCO connected to a resistor as it wasn’t connected to anything prior 
3.      Potential divider resistor (R26)  connected to one of the op amps 
4.      Capacitor C1 connected to resistor (R3) 
5.      Capacitor C3 connected to resistor (R7) 
6.      Capacitor C3 connected to via and then to transistor (Q2) 
7.      Capacitor C18 connected to MOSFET (Q4) 
8.      Capacitor C18 connected to pin 2 of audio amplifier 

Listed above are some of the problems we had which we have now fixed.  However, when we send a signal through the board, we can only find the signal up to the pre amplifier and the switching mixer.  Below are some pictures of the signal going through each of the stages in the circuit.

Firstly when we connect the board to 5V, the VCO sent a signal which had a frequency of approximately 49 kHz (this could be tuned to a value we desired).  This is shown below:



Next, we used the VCO output and fed it into the flip flop. The picture shown below is the output of the flip flop.  It is almost half of the signal from the VCO.



The next stage we checked to see whether the input signal was feeding into the transistor amplifier and into the transistor.   This signal was basically the signal we fed in straight from the function generator.  Although this was not a problem we have added it to show the stages of the circuit.



The output signal from the transistor amplifier was fed into the switching mixer along with the output signal of the flip flop.  At this point the signal that was passing through and the input signals had a lot of noise.  The output signal is shown below:



This signal was then fed into the operational amplifiers which amplified the signal but the signal was then saturated.


The next stage was the audio amplifier, this didn’t give any amplification and there was a lot of noise.


After a lot of fault finding we were unsuccessful and we decided that if we had time at the end of our project, we would come back to this as we needed to start testing our final PCB.  We felt it was unsuccessful because we were getting some graphs on the oscilloscope that we didn’t expect.  Also a lot of noise which we didn’t want which shows it is incorrect.

We have a labVIEW program that works correctly; it can shift the captured signal from a high frequency to a frequency in the audible range.  Initially we were taking steps with our labVIEW program and testing it on the PCB along the way.  At this point we decided to focus on finishing the labVIEW program.   As we started to test our PCB, we realised it wasn’t working as expected.  The +15V and the -15V were short circuiting as were the ground and the 5V.  Also the operational amplifiers were shorting out.  We could not comprehend why our PCB was doing this and so came to the conclusion that maybe because the +15V and -15V had thin connections on the PCB that the board must have been damaged, therefore we have decided to re make the PCB.  This took one day to complete.  This now works and a video of our PCB in action will be posted shortly.

27/07/2012

Update on myDAQ accoustics - myBAT


As stated last week, we needed to work on the AA Filter to improve the filtering.  We did this by tweaking the resistor values and capacitor values until it satisfied our specification.  The datasheet for our Electret microphone reads that it works well until around 66 kHz but goes quite weak to signals above this value.  Therefore we needed an AA Filter which would cut off at approximately 66 kHz and as the myDAQ has an upper limit of 100 kHz, we needed it to attenuate at approximately 100 kHz. 
The pictures below show the frequency response of our AA Filter.  It initially starts at 24 dB and at 21 dB the cut off frequency is approximately 64 kHz shown in the first picture, at 100 kHz it attenuates by approximately 34 dB shown in the second picture.




We were satisfied with our results as they matched our specifications.  The picture below shows the AA Filter built on the breadboard and connected to the myDAQ.


We decided that it was time to start on our final design.  As we are now going to do the shifting on labVIEW there will be less hardware.  Using Altium, we designed the schematics and PCB layout for our final PCB (shown below). We then sent it in to be manufactured.  As you can see from the schematics there are four operational amplifiers.  Three of them are for the AA Filter and one is for the pre-amplifier.  We strived to keep the circuit to four operational amplifiers as we could use a quad operational amplifier chip resulting in less space used as well as less complexity.  This would also help for future students to build this design.





Whilst working on this task we soldered our microphones onto the PCB that we built earlier.  The final parts that we were waiting for have arrived and we have soldered them.  We are going to start testing very soon.  Final PCB for the first design is shown below.




After submitting our design for the final PCB, it was manufactured within a day.  Below is a screenshot showing the PCB after it was manufactured.



We started soldering shortly afterwards.  As this PCB is smaller and has fewer components than the last one, it was reasonably quicker to solder.  Below is a picture of our final PCB.


We have soldered in the microphone and  the wires to connect to the myDAQ.  We wanted the wires to be like this so in the future if we wanted to add more to it or more PCB’s we could connect via the wires.